Awkward adolescence is a subject of some fascination for Argentine director Lucía Puenzo, whose “XXY” and “The Fish Child” both explored the terrain of early sexual awakening. Her new film, “The German Doctor,” also travels this road, focusing on a 12-year-old heroine who crosses paths with one of the 20th century’s most notorious war criminals. The film’s title refers to Nazi physician Josef Mengele, who fled to South America after his inhumane experiments on concentration camp inmates during World War II came to light.

Based on Puenzo’s novel “Wakolda,” the film is set in 1960, during a window of several months about which little historical evidence exists detailing Mengele’s whereabouts or activities. Set in a Patagonian enclave of expatriate Germans, the story centers on the mutual fascination between Mengele (Àlex Brendemühl), who calls himself Helmut Gregor, and Lilith (Florencia Bado), the daughter of an Argentine couple in whose guesthouse Helmut decides to rent a room.

Aside from the title character, only one other character in the film is real: Nora Eldoc (Elena Roger), a real-life Israeli Mossad agent who was known to be hunting him. Lilith’s parents, Eva (Natalia Oreiro) and Enzo (Diego Peretti), on the other hand, are entirely fictional, as is Lilith.

Conflict arises when the doctor notices that Lilith is short for her age and offers to treat her with what he says are growth hormones. Eva, the child of German immigrants, trusts Helmut, played by Brendemühl with a simmering intensity that flips easily between charm and malevolence. She wants her daughter to get the treatment. Enzo, on the other hand, is more wary.

Lilith, for her part, is drawn to Helmut because he’s handsome, exotic and a bit forbidden. “Mom says I do everything that is off limits,” she tells him, when they first meet. Asked if that assessment is true, she replies, “Sort of.”

Helmut is also clearly interested in Lilith and her family, though it’s never fully explained why. Pages from the doctor’s journals, which the film frequently cuts to, are filled with meticulous notes, measurements and clinical drawings of the girl and her parents. (Eva, pregnant with twins, is a secondary obsession of Helmut’s. And Mengele was notorious for his unhealthy interest in twins, on whom he performed gruesome and often fatal experiments.)

What happens in “The German Doctor” — which feels, at times, like a real-life horror story — could have occurred, I suppose. But Puenzo is interested in larger truths than retelling the tale of Mengele. Those truths have to do not only with post-war Argentina, and its seemingly open-door policy toward fugitive Nazis, but also with the nature of adolescent attraction. Mocked by her Aryan classmates for being a “dwarf,” Lilith feels accepted, even loved, by Helmut. His attention — whether prurient or genuine affection — feels empowering to Lilith.

Puenzo has a knack for plumbing the heads and hearts of teenage girls. The director coaxes a mesmerizing, unmannered performance out of Bado, who is making her feature-film debut.

At times, however, the filmmaker’s literary touch is heavier than necessary. Drawing a poetic analogy between Enzo’s hobby of repairing porcelain dolls — a metaphor for human perfection — and Nazi theories of racial purity, “The German Doctor” sometimes pitches its message with a too-explicit spin.

For the most part, though, the film is a quiet knockout. So is its young star. Bado beautifully captures that moment in a girl’s life when she’s not quite ready to let go of innocence, but is starting to flirt with the unknown.

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